[PATCH] Tweak array_at_struct_end_p
Richard Biener
rguenther@suse.de
Thu May 4 09:07:00 GMT 2017
The following picks the changes suggested as followup for PR80533
that do not cause the warning regression on accessing a [0] array.
Additionally the patch removes the unnecessary allow_compref of the
function.
The question whether we want to allow an array to extend into
padding still stands. This patch allows it for C99 flex arrays
(but not pre-C99 GNU extension [0] due to the above warning
regression, also not for [1] or larger arrays we treat as flex arrays
when we can't see an underlying decl).
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2017-05-04 Richard Biener <rguenther@suse.de>
* tree.c (array_at_struct_end_p): Handle arrays at struct
end with flexarrays more conservatively. Refactor and treat
arrays of arrays or aggregates more strict. Fix
VIEW_CONVERT_EXPR handling. Remove allow_compref argument.
* tree.c (array_at_struct_end_p): Adjust prototype.
* emit-rtl.c (set_mem_attributes_minus_bitpos): Adjust.
* gimple-fold.c (get_range_strlen): Likewise.
* tree-chkp.c (chkp_may_narrow_to_field): Likewise.
Index: gcc/tree.c
===================================================================
--- gcc/tree.c (revision 247542)
+++ gcc/tree.c (working copy)
@@ -13227,18 +13235,26 @@ array_ref_up_bound (tree exp)
return NULL_TREE;
}
-/* Returns true if REF is an array reference to an array at the end of
- a structure. If this is the case, the array may be allocated larger
- than its upper bound implies. When ALLOW_COMPREF is true considers
- REF when it's a COMPONENT_REF in addition ARRAY_REF and
- ARRAY_RANGE_REF. */
+/* Returns true if REF is an array reference or a component reference
+ to an array at the end of a structure.
+ If this is the case, the array may be allocated larger
+ than its upper bound implies. */
bool
-array_at_struct_end_p (tree ref, bool allow_compref)
+array_at_struct_end_p (tree ref)
{
- if (TREE_CODE (ref) != ARRAY_REF
- && TREE_CODE (ref) != ARRAY_RANGE_REF
- && (!allow_compref || TREE_CODE (ref) != COMPONENT_REF))
+ tree atype;
+
+ if (TREE_CODE (ref) == ARRAY_REF
+ || TREE_CODE (ref) == ARRAY_RANGE_REF)
+ {
+ atype = TREE_TYPE (TREE_OPERAND (ref, 0));
+ ref = TREE_OPERAND (ref, 0);
+ }
+ else if (TREE_CODE (ref) == COMPONENT_REF
+ && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 1))) == ARRAY_TYPE)
+ atype = TREE_TYPE (TREE_OPERAND (ref, 1));
+ else
return false;
while (handled_component_p (ref))
@@ -13246,19 +13262,42 @@ array_at_struct_end_p (tree ref, bool al
/* If the reference chain contains a component reference to a
non-union type and there follows another field the reference
is not at the end of a structure. */
- if (TREE_CODE (ref) == COMPONENT_REF
- && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 0))) == RECORD_TYPE)
+ if (TREE_CODE (ref) == COMPONENT_REF)
{
- tree nextf = DECL_CHAIN (TREE_OPERAND (ref, 1));
- while (nextf && TREE_CODE (nextf) != FIELD_DECL)
- nextf = DECL_CHAIN (nextf);
- if (nextf)
- return false;
+ if (TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 0))) == RECORD_TYPE)
+ {
+ tree nextf = DECL_CHAIN (TREE_OPERAND (ref, 1));
+ while (nextf && TREE_CODE (nextf) != FIELD_DECL)
+ nextf = DECL_CHAIN (nextf);
+ if (nextf)
+ return false;
+ }
}
+ /* If we have a multi-dimensional array we do not consider
+ a non-innermost dimension as flex array if the whole
+ multi-dimensional array is at struct end.
+ Same for an array of aggregates with a trailing array
+ member. */
+ else if (TREE_CODE (ref) == ARRAY_REF)
+ return false;
+ else if (TREE_CODE (ref) == ARRAY_RANGE_REF)
+ ;
+ /* If we view an underlying object as sth else then what we
+ gathered up to now is what we have to rely on. */
+ else if (TREE_CODE (ref) == VIEW_CONVERT_EXPR)
+ break;
+ else
+ gcc_unreachable ();
ref = TREE_OPERAND (ref, 0);
}
+ /* The array now is at struct end. Treat flexible arrays as
+ always subject to extend, even into just padding constrained by
+ an underlying decl. */
+ if (! TYPE_SIZE (atype))
+ return true;
+
tree size = NULL;
if (TREE_CODE (ref) == MEM_REF
Index: gcc/tree.h
===================================================================
--- gcc/tree.h (revision 247542)
+++ gcc/tree.h (working copy)
@@ -4885,12 +4885,10 @@ extern tree array_ref_up_bound (tree);
EXP, an ARRAY_REF or an ARRAY_RANGE_REF. */
extern tree array_ref_low_bound (tree);
-/* Returns true if REF is an array reference to an array at the end of
- a structure. If this is the case, the array may be allocated larger
- than its upper bound implies. When second argument is true considers
- REF when it's a COMPONENT_REF in addition ARRAY_REF and
- ARRAY_RANGE_REF. */
-extern bool array_at_struct_end_p (tree, bool = false);
+/* Returns true if REF is an array reference or a component reference
+ to an array at the end of a structure. If this is the case, the array
+ may be allocated larger than its upper bound implies. */
+extern bool array_at_struct_end_p (tree);
/* Return a tree representing the offset, in bytes, of the field referenced
by EXP. This does not include any offset in DECL_FIELD_BIT_OFFSET. */
Index: gcc/emit-rtl.c
===================================================================
--- gcc/emit-rtl.c (revision 247542)
+++ gcc/emit-rtl.c (working copy)
@@ -1957,7 +1957,7 @@ set_mem_attributes_minus_bitpos (rtx ref
|| (TREE_CODE (t2) == COMPONENT_REF
/* For trailing arrays t2 doesn't have a size that
covers all valid accesses. */
- && ! array_at_struct_end_p (t, false)))
+ && ! array_at_struct_end_p (t)))
{
attrs.expr = t2;
attrs.offset_known_p = false;
Index: gcc/gimple-fold.c
===================================================================
--- gcc/gimple-fold.c (revision 247542)
+++ gcc/gimple-fold.c (working copy)
@@ -1235,7 +1224,7 @@ get_range_strlen (tree arg, tree length[
the NUL.
Set *FLEXP to true if the array whose bound is being
used is at the end of a struct. */
- if (array_at_struct_end_p (arg, true))
+ if (array_at_struct_end_p (arg))
*flexp = true;
arg = TREE_OPERAND (arg, 1);
Index: gcc/tree-chkp.c
===================================================================
--- gcc/tree-chkp.c (revision 247542)
+++ gcc/tree-chkp.c (working copy)
@@ -3277,7 +3277,7 @@ chkp_may_narrow_to_field (tree ref, tree
return DECL_SIZE (field) && TREE_CODE (DECL_SIZE (field)) == INTEGER_CST
&& tree_to_uhwi (DECL_SIZE (field)) != 0
&& !(flag_chkp_flexible_struct_trailing_arrays
- && array_at_struct_end_p (ref, true))
+ && array_at_struct_end_p (ref))
&& (!DECL_FIELD_OFFSET (field)
|| TREE_CODE (DECL_FIELD_OFFSET (field)) == INTEGER_CST)
&& (!DECL_FIELD_BIT_OFFSET (field)
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